Allow for the vnode in the virt_agents entries to be a "wildcard"

(okay, a "*") in which case it means to not insert a specific node_id
into the event, but rather leave it to the subscribers to specify
what they need (in the case of the delay agent pid/eid/lan/lan-vnode.
The new assign_wrapper inserts these entries like this. Old stuff will
continue to work of course.